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Laser-based spectroscopy and spectrometry were extensively investigated in nanoscience, materials science, biomedical science, and etc. Different lasers with wavelengths from ultraviolet to infrared, and with duration from continuous-wave (CW) to femtoseconds have been employed in various spectroscopic techniques to investigate the properties of materials and nanostructures. However, the sensitivity, spectral resolution, and spatial resolution of these techniques still need to be improved to better serve the purposes of detecting and analyzing various materials. The objective of the research in this dissertation is to improve the sensitivity, spectral resolution, and spatial resolution of different laser-based spectroscopy and spectrometry techniques, such as tip- and surface-enhanced Raman spectroscopy (TERS and SERS), coherent anti-Stokes Raman spectroscopy (CARS), optical emission spectroscopy (OES), laser-induced breakdown spectroscopy (LIBS), and laser-assisted mass spectrometry (LAMS).
(1) To overcome the diffraction limit of light, a TERS system, using an apertureless metallic tip as a near-field probe, was built for measuring nanoscale materials and structures. (2) Gold-coated horizontally aligned carbon nanotubes (Au-HA-CNTs) were fabricated as a new type of SERS active substrate by using laser-assisted chemical vapor deposition (LCVD), followed by a sputtering coating process. (3) A broadband CARS system was built with a Ti:sapphire femtosecond (fs) laser as pump (ωp) and a photonic crystal fiber (PCF) as a white light source for Stokes beam generation (ωs). (4) OES of combustion flames for diamond synthesis was carried out with laser resonant excitation (by a wavelength-tunable continuous wave (CW) CO2 laser at a wavelength of 10.532 µm to resonantly excite the CH2-wagging vibrational mode of the C2H4 molecules). (5) High-temperature and low-density plasmas were generated for improved spectral resolution in LIBS. (6) Laser-assisted mass spectrometry was realized using laser ionization combined with metastable ionization in open air for solid material measurement. In summary, the research on laser-based spectroscopy and mass spectrometry has rendered improved performance in sensitivity, spectral resolution, or spatial resolution, which are significantly important for the development of characterization techniques for various novel materials and structures.
Adviser: Yongfeng Lu